The present invention generally relates to semiconductor packages, and more specifically relates to a semiconductor package construction aimed at improving thermal performance.
To improve the thermal performance of a flipchip semiconductor package, a few companies are adding metal alloys between the heatspreader and the die, as the metal alloys conduct heat better than the heatspreader. The metal alloys are metallurgically bonded to the heatspreader and the silicon (i.e., on the die). To get the metallurgical bonding, a coating is needed on the silicon so that a bondable surface is provided for the metal alloy to form a metallurgical bond. The problem with this approach is that today's semiconductor fabrication laboratories are not equipped in terms of both equipment and process to provide the coating which is needed. Generally, performing additional steps (i.e., performing an additional process) within a semiconductor fabrication process costs more than adding a process to the back end process (like packaging).
Another problem with the foregoing approach is illustrated in FIG. 1: the die 10 tends to decouple from the heatspreader 12 (in FIG. 1, reference numeral 14 identifies the substrate). Generally, the larger the die, the higher the die backside warpage. Since the die is free to bend and warp, the contact between the die and the heatspreader is reduced, thereby decreasing the thermal performance.
As such, the foregoing approach provides the following disadvantages:                1) the cost of adding a process to the overall semiconductor fabrication process is high; and        2) the die tends to warp and decouple from the heatspreader, resulting in a reduction in thermal performance.        